1. Field of the Invention
This invention relates generally to the field of wireless communication using a space-time block coded (STBC) multiple input multiple output (MIMO) scheme and, more particularly, to array processing using an aggregate channel matrix generated using a space-time block code structure.
2. Description of the Related Art
Owners and/or operators of communication networks, i.e., the service providers, are constantly searching for methods and equipment that can meet the changing needs of their subscribers. Subscribers of communication networks, including wireless communication networks, require higher information throughput in order to exploit the expanding range of services being provided by current communication networks. For example, wireless communication subscribers are now able to have simultaneous access to data networks such as the Internet and to telephony networks such as the Public Switched Telephone Network (PSTN). Also, service providers are constantly investigating new techniques that would allow them to increase their information transfer rate.
Information transfer rate is the amount of information, usually measured in bits per second, successfully conveyed over a communication channel. The information transfer rate can be increased in a number of well known manners. One technique is to increase the power of the transmitted signals. A second technique is to expand the frequency range (i.e., bandwidth) over which the communication is established. However, both power and bandwidth are limited by certain entities such as governmental and standards organizations that regulate such factors. In addition, for portable devices, power is limited by battery life.
An approach that circumvents the power and bandwidth limitations is to increase the number of antennas used to transmit and receive communication signals (i.e., employing a multiple input multiple output (MIMO) system). Multiple antenna diversity has been an effective way to combat fading signals in land mobile communication systems. Typically, the antennas are arranged as an array of antennas. One of the main features of MIMO systems is that they benefit from the multipath propagation of radio signals. In a multipath environment, radio waves transmitted by an antenna do not propagate exclusively in straight lines towards the receive antenna. Rather, the radio waves scatter off a multitude of objects that block the direct path of propagation. Thus, the environment creates a multitude of possible paths from transmit to receive antennas. These multiple paths interfere with each other at the location of the receive antenna. This interference process creates a pattern of maxima and minima of received power, with the typical spatial separation between consecutive maxima being approximately one wavelength.
MIMO systems exploit the rich scattering environment, and use multiple transmitters and receivers to create, in effect, a plurality of parallel subchannels each of which carries independent information. For transmitting antennas, the transmitted signals occupy the same bandwidth simultaneously and thus spectral efficiency is roughly proportional to the number of subchannels. For receiving antennas, MIMO systems use a combination of linear and nonlinear detection techniques to disentangle the mutually interfering signals. Theoretically, the richer the scattering, the more subchannels that can be supported.
While MIMO techniques theoretically allow antenna arrays to have relatively high information rates, the actual achieved information transfer rate will greatly depend on how the information is coded in the different subchannels. The information transfer rate of the system increases as the number of antennas in a transmit and/or receive array is increased. However, in many cases the amount of space available for the antenna array is limited. In particular, the space limitation is very critical for portable wireless devices (e.g., cell phones, Personal Digital Assistants (PDAs), and the like). Increasing the number of antennas in an array of limited space decreases the spacing between individual antennas in the array. The reduced spacing between antennas typically causes signal correlation to occur between signals received from different antennas. Signal correlation reduces the gain in information transfer rate obtained by the use of MIMO techniques.
One technique for using antenna arrays in a MIMO implementation is a space-time transmit diversity technique. Space-time transmit diversity (STTD) coding uses two or more transmitting antennas in order to take advantage of both the spatial and temporal diversity of the channel. An array of antennas is typically divided into groups (i.e., spatial diversity) and each group is assigned a plurality of time instances for transmission (i.e., time diversity). Various space-time block coding (STBC) techniques are well-known to those of ordinary skill in the art. Typical space-time block decoding techniques require that all symbols from the same codewords be received before decoding can be performed. As the number of transmit antennas increases, so does the size of the codeword. Accordingly, the wait time required to receive all the codewords prior to decoding increases, resulting in greater latency. Also, longer codewords require greater computational complexity.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.